This proposal seeks support for our studies on the mechanisms of glyoxalase I and lactage racemase. We believe that these enzymes bear some mechanistic similarities, i.e., fast-shielded proton transfers to thioester-stabilized carbanion intermediates. We have recently synthesized the heretofore unreported fluoromethylglyoxal and have demonstrated that this compound undergoes a unique glyoxalase I-catalyzed partitioning between protonation of an ene-diolate intermediate (fluorolactate formation) and fluoride-elimination (pyruvate formation). We propose to synthesize othe unusual halogenated alpha-ketoaldehydes as 1) mechanistic probes for glyoxalase I from various sources, 2) potential suicide inhibitors of this enzyme and 3) possible new antineoplastic agents. These experiments will enhance our understanding of this unusual enzyme system. Lactate racemase has been proposed to effect racemization of lactic acid by hydride transfer mechanisms via a thioester intermediate. We suggest that this reaction occurs by a highly shielded proton transfer mechanism via a possible thioester intermediate and propose a reevaluation of this enzyme to determine 1) if a thioester is formed and the mechanism of its ATP-independent formation, 2) if a hydride or proton transfer mechanism is operative and 3) the nature of the active site functionalities which catalyze this reaction. Together with the glyoxalase studies, these experiments will provide important mechanistic information on two interesting hydrogen transfer reactions.